This invention relates to improvements in or relating to mirrors which are intended to be bonded to a substantially rigid support surface, for example a wall, a door or a substantially rigid backing board.
There is considerable interest in the artistic and architectural possibilities of structures obtained by laminating mirrors to support surfaces, especially the internal and external walls of buildings. However, there is a tendency for the products so obtained to fracture when exposed to an environment in which substantial variations in temperature are encountered; for example such as when the product comprises outside cladding for a building or is otherwise exposed to the elements and/or to direct sunlight. The problem is particularly acute when employing large mirrors, especially where the transparent face is provided by a sheet of glass. To overcome this defect it has been proposed to include a flexible and resiliently compressible layer of a polymeric foam which is bonded to the layer of reflecting material and in use lies between the mirror and the surface to which it is laminated; see GB-A-2048166.
This foam interlayer absorbs the stresses developed during heating or cooling of the mirror and the surface to which it is attached due to the different coefficients of expansion of the mirror and the surface, thereby reducing or preventing fracture of the mirror. The foam layer also provides the mirror with valuable shock absorbant characteristics which reduce its tendency to fracture on impact. Further, and very importantly, where the transparent face is glass and fracture occurs, it has been found that the glass fragments tend to remain bonded to the foam layer, thereby reducing the danger of damage to property or persons by flying or falling glass, and substantially improving the safety aspects of the product.
Mirrors backed with such foam layers have therefore found rapid acceptance in the market and are especially valuable in applications where safety is paramount.
We have found however the components of the adhesives used to bond such foam layer-backed mirrors to the support surfaces tend to infiltrate the foam to the detriment of the foam itself, the reflecting coating of the mirror and/or the adhesive employed to bond the mirror to the foam. For example, where commonly used contact adhesives are used to bond the foam-backed mirror to the support surface, solvents in the adhesive (or vapours thereof) tend to pass through the foam and attack the bond between it and the mirror, thereby causing the foam to delaminate from the mirror.
There is therefore a need to develop some means for preventing these components of the adhesive from contacting the foam or its bond with the reflecting layer of the mirror. However, any barrier layer must itself be unaffected by these components and must bond well to the adhesive and to the foam layer. Further, it must of course be capable of being bonded to the foam layer by means other than an adhesive having components which are capable of attacking the foam layer and/or its bond with the reflective layer of the mirror.
We have now found that these requirements are satisfied by heat bonding a flexible and substantially impermeable polyurethane skin to the exposed face of the foam layer.